1. Field of the Invention
The present invention relates to a reference voltage generating circuit for generating a stable reference voltage with low power consumption, which voltage is suitable for use in an integrated circuit.
2. Prior Art
An example of known reference voltage generating circuit used in an integrated circuit is shown in FIG. 1. This reference voltage generating circuit is comprised of a voltage dividing circuit formed of a series circuit of resistors R51 and R52 provided between a power source VDD and a power source VSS, and a low-pass filter formed of a resistor R53 and a capacitor C. The low-pass filter integrates the output voltage of the voltage dividing circuit to provide a reference voltage output VREF. In order to reduce the power consumption, resistors having large resistance values are used as the voltage dividing resistors R51, R52. The low-pass filter serves to produce a stable reference voltage VREF from the output voltage of the voltage dividing circuit. To this end, the time constants of the resistor R53 and capacitor C are set to large values.
In the reference voltage generating circuit described above, it is necessary to set the time constant of the low-pass filter to be sufficiently large so as to obtain a stable reference voltage VREF. More specifically, a resistor having a large resistance value of 50 k.OMEGA. may be used as the resistor R53, and a capacitor having a large capacitance of 22 .mu.F may be used as the capacitor C. This may cause a problem of a delay in the rise of the reference voltage VREF when the power is turned on. The capacitor C is located outside the integrated circuit, and connected to the interior of the integrated circuit.
Although the rising speed of the reference voltage VREF may be increased by reducing the time constant of the low-pass filter, this would make the reference voltage VREF unstable.